Photoelectric cell installation for signal system and method of installing same



-Sheec 1 Jvrewrae E 2 Sheets Dec. 9. 1969 E. A. GRISWOLD PHOTOELECTRIC CELL INSTALLATION FOR SIGNAL SYSTEM AND METHOD OF INSTALLING SAM Filed Sept. 21, 1965 czaw/wa A. @Q/swan E. A. GRISWOLD 3,483,507 PHOTOELECTRIC CELL INSTALLATION FOR SIGNAL Dec. 9. 1969 SYSTEM AND METHOD OF INSTALLING SAME 2 Sheets-Sheet 2 Filed Sept. 21, 1965 United States Patent C) M PHOTOELECTRIC CELL ILISTALLATION FOR SIGNAL SYSTEM AND METHOD OF IN- STALLING SAME Edward A. Griswold, 2071 E. Galbreth Road, Pasadena, Calif. 91107 Filed Sept. 21, 1965, Ser. No. 488,946 Int. Cl. G08g 1/04 US. Cl. 34038 Claims ABSTRACT OF THE DISCLOSURE The present invention relates generally to an electrical system for sensing the movement or passage of a vehicle or other object; and more particularly to a system of this type including a photoelectric cell which may be designed to operate an alarm or signal in response to a change in light incident on the cell, as, for example, a vehicle entering a service station.

There is a well-known and widely recognized need in automobile service stations, as a typical example, of a system to signal the arrival of an automobile or a truck at the fuel pumps for re-fueling or other service. A signal system of this type has many advantages since it alerts operating personnel immediately to the arrival of a potential customer and permits service to be rendered more promptly and without any delays irritating to the customer. Signal systems of this character generally require some type of remote operation in order to remove from the vicinity of the fuel pumps, which is considered a hazardous area, any electrical connections or electrical equipment which use enough power to cause a spark and therefore to create a hazardous condition.

Various types of systems have been installed including some component or member in the path of the vehicle to activate the signal system in response to travel of the vehicle. One example of a widely used type of signal system is an elastic tube stretched across the driveway at the fuel pumps and which is compressed by travel of the vehicle over the tube, the increased air pressure within the tube activating electric switches at a position outside the hazardous area.

A particular disadvantage of this type of installation is that the elastic tube is loose and can easily be carried away from its proper position unless it is anchored down in some way. Whether loose or anchored, the tube projects above the otherwise smooth surface of the driveway and constitutes a hazard to pedestrian travel. A hazard of this character to operating personnel, and particularly to customers walking on the driveway and perhaps less observant than an employee, is to be avoided whenever possible.

Another disadvantage of signal systems including an elastic tube of this type is that they frequently malfunction and require a substantial amount of maintenance, because of deterioration from wear in normal usage and from weathering since they are exposed to the sun, rain, and a full range of temperature changes.

As an alternative arrangement, photoelectric cells have 3,483,507 Patented Dec. 9, 1969 been tried but all such installations known to applicant have suffered from various disadvantages, chiefly the fact that they are particularly subject to false alarms. If the photoelectric cell is made too sensitive, it is triggered by transient changes, such as the shadow of a person walking by the cell, or any other random shadow which affects the change in the light incident on the cell. On the other hand, if this problem is countered by making the cell less sensitive, then known types of systems are oftentimes found to be insensate under the same ambient light conditions.

It is a general object of the invention to provide an improved system for sensing the movement of an object, such as a vehicle, by the change in incident light thereby created on an element of the system.

It is also a general object of the present invention to provide an installation of a photoelectric cell for an alarm system which effectively removes from the driveway adjacent the fuel pumps all protrusion or projections above the normal plane surface of the driveway, thereby eliminating any object over which a pedestrian or customer may trip and fall.

It is an object of the present invention to provide a photoelectric cell installation for an alarm system of the character described which responds promptly and accurately to the presence of a vehicle but which is not triggered to render false alarms by smaller objects or transient shadows cast on the cell.

A further object of the invention is to provide a photoelectric cell installation of the character described which is easy and simple to install and yet which is of a character that it can be used safely in a hazardous area such as the apron of a driveway adjoining fuel pumps where flammable liquids are often spilled on the driveway.

A further object of the present invention is to provide a novel construction for the installation of a photoelectric cell of the character described which is reliable in operation and simple to maintain, allowing parts to be repaired and replaced expeditiously.

These objects of the present invention are achieved by placing in a driveway over which vehicles pass a photoelectric cell which is set in the driveway in such a position that light normally incident thereon is intercepted by a vehicle passing over the cell, the cell being connected by an electric circuit to an alarm of either visual or audible type and responsive to the change in the light incident on the cell. The photoelectric cell is set in the driveway in such a manner as to be substantially flush with but just below the surface of the driveway, thereby providing for access of light to the cell over a maximum possible light-gathering angle. It is considered desirable that this angle amount to a solid angle of at least or thereabouts, but it is entirely practical to increase this angle to the range of 150, thus approaching rather closely the ideal maximum of In a preferred embodiment of the invention, the installation includes a tubular member set into the driveway and terminating below the surface of the driveway; a housing slidably received in the tubular member and supported thereon; and a photoelectric cell in the housing adjacent a light-transmitting opening in the upper end of the housing. While the photoelectric cell is sealed in the housing and the housing in turn is sealed in the tubular member by a suitable cement or sealing compound in order to prevent access by liquids to the interior of the housing and light cell, the housing is easily removed from the upper end of the tubular member for repair and maintenance. To permit this, the electric conductor leading into the tubular member is provided with sufiicient slack to allow the housing to be fully Withdrawn from the tubular member.

How the above and other objects and advantages of the present invention are achieved will be more fully understood by reference to the following description and to the annexed drawings, in which:

FIG. 1 is a plan view of a typical service station installation showing the location of light cells in the apron or driveway adjoining the fuel pumps.

FIG. 2 is an enlarged fragmentary vertical section on line 2-2 of FIG. 1.

FIG. 3 is a further enlarged fragmentary section similar to FIG. 2.

FIG. 4 is a fragmentary vertical section through the concrete and the light cell installation showing a variational form of the invention.

FIG. 5 is another fragmentary vertical section showing a further variational form of theinvention.

FIG. 6 is a fragmentary plan'view of a variational form of the invention.

FIG. 7 is a fragmentary vertical section on line 77 of FIG. 6.

FIG. 8 is a perspective of a wrench for turning the polarizing disc of FIG. 6.

FIGS. 9 and 10 are, respectively, a fragmentary plan and longitudinal section on line Iii-4t of FIG. 9 of another embodiment of the invention.

FIG. 11 is a perspective of a further embodiment of the invention.

FIG. 12 is a fragmentary vertical section on line 12-12 of FIG. 11.

Referring now to the drawings, and more particularly to FIG. 1, there is shown a plurality of photoelectric cells 10 which are installed individually in spaced positions in a highway, driveway or other traffic-supporting surface indicated generally at 11. The driveway typically consists of a concrete apron 12 in the vicinity of the fuel pumps 14 which are typically placed on a raised island 15 to protect them against being damaged by a vehicle. The approaches to concrete apron 12 are generally an asphalt macadam or similar type of hard surfacing, the concrete being preferred in the vicinity of the fuel pumps not only because it is more resistant to oil, gasoline, and other petroleum that may be spilled upon it, but also because it is harder and more firm, therefore less likely to be indented by heavy vehicles standing on it. However, the driveway in which the photoelectric cells are installed may, within the scope of the present invention, be all of any one material, either asphalt or concrete. In general, the top surface 12a of the driveway or the like is generally horizontal, but this should be interpreted to include ramps or the like.

Each light cell 10 is connected by a buried conductor 16 passing through a common conduit 18 to a. box 19 suitably located inside a building or otherwise removed from the hazardous area around pumps 14 and which contains the alarm and is connected to a suitable source of power.

In many instances, the light cells will be installed in existing driveways, although provision will ordinarily be made for installation prior to pouring a concrete driveway if such an installation is anticipated. FIGS. 2 and 3 show in enlarged vertical section a typical installation which is adapted to existing driveways. Assuming concrete driveway 12 having already been poured and set, the first operation is to drill a hole 20 downwardly from the upper traffic-engaging surface 12a over which vehicles pass. The axis of hole 20 is preferably vertical or nearly so and is of a diameter to take easily a tubular housing 22. A layer 23 of a suitable cement or mastic is preferably placed between housing 22 and the wall of hole 20 in order to provide a fluid-tight connection between the tubular member and the concrete, thus excluding from housing 22 water or any other liquids that might fall upon top surface 12a of the drive. There are various suitable cements or sealing compounds of either hardening or nontypical cement that has been found satisfactory in use is an epoxy resin, such as form-a-gasket number 1 produced by Permatex Company, Inc.

The upper end of tube 22 is positioned a short distance below top surface 12a of the driveway, as shown in FIG. 3. Into this upper end of the tube is inserted the housing 25 for the photoelectric cell, the housing preferably being an easy sliding fit within tubular member 22. As may be seen particularly in FIG. 3, the upper end of housing 25 is provided with an annular flange 25a which extends outwardly around the housing at or just above the upper end of tube 22. A layer of sealing compound 24 is placed around light housing 25 between it and tube 22; and the sealing compound preferably extends between flange 25a and the end of tube 22 in order to provide a moistureftight seal for electrical connections and to assist in holding the housing 25 in place within the tubular sleeve.

The layer of sealing compound 24 is preferably a nonhardening compound such as av non-hardening epoxy resin, an example of which is form-.a-gasket number 2 manufactured by Permatex Company, Inc. The thickness of flange 25a and the spacing of the end of tube 22 below surface 12a are such that the upper end of cell housing 25 is flush or substantially coplanar with surface 12a, as shown in FIGS. 2 and 3. Thus, the housing rests upon and is supported by the surrounding sleeve which positions the housing to locate the upper end'of the housing in the manner described.

Inside housing 25 is a photoelectric cell 27. Although the invention is not limited to any particular type of photoelectric cell, it is preferred to use a photoconductive or resistance type of cell in this system. From the bottom of cell 27 a pair of leads 28 enter plug 29 for connection to externally accessible plug terminals 30. To these terminals 30 are connected two wires of the insulated conductor 16, the terminals normally being then covered by a suitable means such as cap 31 which is screwed onto the base of plug 29. Cap 31 is preferably filled with a mastic or non-hardening sealing compound to cover the metal connections and insulate them from moisture.

Tubular member 22 is slotted axially at one side in order to permit conductor 16 to pass through the slot and reach box 19. A slot of this character is indicated at 32 as preferred to a round hole or the like in the wall of housing 25 as it makes installation of the tubular member and the conductor easier.

Assuming that drive 12 is already in existence, a narrow slot 35 is cut in the drive extending downwardly from top surface 12a to a suflicient depth to pass the upper end of slot 32. This slot terminates at one end at hole 20 and at the other end at any point convenient for access to box 19. This slot need only be wide enough to receive conductor 16 which is laid in the slot, the depth of the slot in the driveway being suflicient to receive the conductor where it comes out of tubular member 22. As seen in FIG. 1, several conductors may be placed in a common conduit 18, which may be only a slot or trench as just described. After the rest of the installation is completed, the slot is back-filled with a suitable mastic or mortar 36 in order to bury conductor 16 and isolate it from damaging contact with moving objects, fluids, and the like.

It will be noted that tubular housing 22 and hole 20 are somewhat deeper than slot 35 in the concrete, thus allowing a limited amount of excess conductor 16 to be stored in a coil 160 or other configuration in tube 22 beneath cell housing 25, as shown particularly in FIG. 2. This excess length of conductor is sufficient in length to equal or to exceed the vertical length of housing 25 so that the housing can be withdrawn from tubular member 22, and so become completely accessible for repair hardening types that may be used for this purpose, a and/or replacement of parts,

Cell housing 25 has a downwardly facing shoulder at 37 which engages the upper end of photoelectric cell 27 to locate the cell a short distance below the plane of driveway surface 12a, the object being to get the photoelectric elements of the cell as close to the driveway surface 12a as practical, and yet locate them slightly below the surface for protection.

Light cell 27 is preferably spaced above plug 29 and is held against the shoulder 37 by the spring-like action of wire leads 28. The wire leads are preferably twisted, by rotating cell 27 slightly to give them a spiral-like configuration. The cell can then be depressed by force from above, yielding without damage. Of course, other resilient support means for the light cell may be provided to support the photoelectric cell with its top surface substantially flush with but preferably slightly below surface 12a on which vehicles are supported. The axis of light cell 27 is preferably vertical in order to eliminate any directional characteristics.

Above photoelectric cell 27, the interior bore of housing 25 is closed by a transparent window 38 which is necessarily light-transmissive in order to permit light from above the driveway to reach the cell in housing 25. Any suitable transparent material may be used for this purpose, but it is preferred to use some of the transparent synthetic resins, such as some of the acrylics. This lighttransmitting window is made of only sufiicient thickness to have the physical strength required to resist breaking; but ordinarily it need not be more than about to 4:, inch thick. It is cemented in place flush with the upper end surface of housing 25.

Immediately below the window 38 is mask 39 which is only partially light-transmissive. This mask is used to control the amount of incident light actually reaching photocell 27. The mask may be a homogeneous material that is translucent or it may be an opaque material having transparent areas, such as small holes in it, or a combination of both. The purpose of mask 39 is to establish a variable control over the amount of incident light passed to the photocell, thus accmplishing either or both of two purposes. In the first place, photocells have a certain amount of variance in their resistivity and consequently it is more practical to compensate for this by changing the amount of incident light on the photocell. The other advantage of this arrangement is that it permits the installer to compensate for local conditions, thus permitting a single cell to be used under a Wide range of light conditions, as, for example, under a canopy where there is less direct light than would be the case if the same cell were installed in an open driveway in direct sunlight.

One of the shortcomings of many earlier types of installations has been the tendency to give false signals. While this has been ascribed to the sensitivity of the photocells, it has actually been in many cases caused by the type of installation and location of the cell so that it responds to transient signals, such as an individual walking past the cell as opposed to an automobile or vehicle and causing the cell to actuate the signal system. This characteristic of the signal system has been substantially eliminated in the present invention.

The light cell is so located that it is facing upwardly and therefore receives a maximum amount of illumination by day or even from artificial sources above the ground and at the same time is located very close to the top surface of driveway 12a so that the light cell has the maximum light-gathering angle 40 as indicated in FIG. 3. This light-gathering angle 40 is, of course, a solid angle since light reaches the cell from all directions. It is designed to have a minimum value of 90 and it is practical in many installations to reach 120l40. The precise angle is, of course, a function of the distance that the photocell elements of cell 27 are located below the plane of surface 12a and also the diameter of the opening occupied by window 38. For a given depth of the cell below surface 12a, the solid angle in which light reaches the cell is increased by increasing the diameter of window 38; or for a given diameter of the window, the angle is likewise increased by moving the cell upwardly, decreasing the thickness of window 38. Ideally, light should be gathered over an entire hemisphere having a solid angle of 180; but this is often not practical since it is usually desired to have no protrusions above the plane of surface 12a and at the same time to afford complete protection to the light cell.

Having a large light-gathering angle as mentioned results in light reaching the cell at the same time from many different directions and the cell is not activated by transient shadows from small objects such as an individual walking past or even over the cell. This is because the shadow cast by an individual reduces the total light reaching the cell by only a very small percentage. It requires an automotive vehicle passing over the cell, and thereby eliminating substantially all the light directly incident on the cell, to cause it to activate the alarm system. As is Well known, vehicles currently have rather low road clearance and provide an area of several square feet over which light is largely blacked out. An object of this size is adequate to block almost all of the light within the solid angle 40.

Of course, a hole as at 20 can be molded in the concrete when it is poured by inserting a suitable form so that the hole 20 may be formed by means other than drilling. However, in the event that installation of a light cell of this character is anticipated before the concrete is poured, it is generally preferable to provide for leading the conductor 16 to the light cell housing through a suitable conduit 42 as shown in FIG. 4. This conduit is placed before the concrete is poured and is then buried in the concrete. The conductor 16 can then be pulled into conduit 42 after the concrete has hardened. The end of the conduit receives housing 25 in the same manner as described above in connection with tubular member 22, the installation being generally similar. Of course, as before, the upper end of cell housing 25 is so positioned with respect to the finished grade of surface 12a of the driveway that it is flush with traffic surface 12a.

Except as specifically noted, the installation of the light cell in a driveway in a length of conduit 42 placed prior to pouring the concrete is essentially the same as already described in connection with FIG. 3. Of course, there is no longer a need for the slot since conductor 16 leaves the conduit through the open end thereof.

Although the installation as last described is preferred under some circumstances, the invention is not necessarily limited to all of these same features. For example, there is shown in FIG. 5 a variational form of the invention which combines structures already described and adds some others, while it also permits placement prior to pouring the concrete. It produces the desired location of the light cell with reference to the top surface of the driveway but differs in details of the installation from those already described.

In FIG. 5, the wires of conductor 16 are connected to terminals of a plug 45 which is cemented in place inside the rigid sleeve or tube 46 with a non-hardening sealing compound as described above. Sleeve 46 serves as an extension of conduit 42 with the sleeve 46 cemented in the open end of conduit 4-2. If sleeve 46 is used also as a form around which the concrete is poured, it may be greased or otherwise suitably coated so that the sleeve does not adhere to the surrounding concrete tightly enough to prevent its removal for servicing. The base of the sleeve is filled with a sealant 48 to cover and protect the connection of the conductor to the terminals 49 on plug 45. Plug 45 is provided with two metal sleeve terminals 49 which are designed to receive slidably prongs 50 projecting downwardly below cell housing 25b which contains a light cell in the manner already described. In this case, the leads from the photocell are connected to prongs 50 and the entire housing can be inserted and removed from the end of tubular sleeve 46. In so doing, the circuit is broken by removing prongs 50 from the terminals 49 of plug 45.

Various changes in the details, construction and installation of the li ht cell are possible, and a few of these will now be illustrated and described. For example, there is shown in FIGS. 6 and 7 a light cell installation which is similar to that illustrated in FIG. 3, except that the light-admitting window and the light mask for controlling the quantity of light admitted to light cell 27 have been replaced by a pair of plane-polarizing plates 55 and 56 controlling light admission. Plates 55 and 56 may be discs of the well-known light polarizing material commonly known as Polaroid which transmit a maximum amount of light when their axes are aligned but which transmit a minimum amount of light when their axes are rotated 90 relative to each other.

As shown in FIG. 6, upper disc 55 is provided with peripheral notches which may be engaged by projecting fingers 58 on tool 69, by lowering the tool of FIG. 8 from the dotted line position of FIG. 7. Using the tool, the top disc can be rotated an any desired position to admit to light cell 27 the desired maximum of light, after which the upper disc can be held in the adjusted position by filling peripheral indentations with a suitable sealant which also operates to hold the disc in place.

Although two physically distinct members are here used to regulate the amount of light transmitted to the light cell, the functions of admitting light and conrolling the amount of light so admitted are combined into these two members rather than performed by separate members as in the form of the invention described in FIG. 3.

FIGS. 9 and 10 illustrate a variational arrangement in which the upper polarizing disc 55a is made without peripheral indentations but is of slightly reduced diameter as compared with the diameter of the circular recess 61 in the light cell housing. The annular clearance between the polarizing disc and the cell housing permits the disc to be rotated freely into the desired position relative to disc 56 beneath it, after which the upper disc is secured in place by filling the angular space around it with sealant, as indicated at 62 in FIG. 10.

The forms of the invention shown in FIGS. 7 and 10 both have the advantage that they are easily adjustable in the field to operate properly under the exact light conditions encountered at the site of installation; and a continuous gradation of light transmission through the polarizing discs 55 and 56 can be obtained between maximum and minimum values by relative rotation of the discs.

Suitable epoxy resin cements are available which are highly satisfactory for a sealant and cement for the discs and which can be removed by a suitable solvent. Removal of the resin permits subsequent adjustment of the value of the transmitted light reaching cell 27 without removing the entire unit or replacing it.

The installations of the light cells previously described have all contemplated permanent installations in areas subjected to tratfic where it is desired to eliminate any significant projections above the tratfic surface. However, for temporary installations or use in locations where traffic is relatively light and consequently minor irregularities in otherwise planar tratlic surface are not objectionable, the installation shown in FIGS. 11 and 12 may be used. Here the supporting structure for the light cell 27 is a thin, disc-like structure 65 which may be molded or cast from a suitable material, such as a synthetic resin or metal.

Disc 65 is preferably little thicker than is necessary to accommodate the light cell 27 and the connections thereto and preferably has a convex upper surface, thus giving to the disc a low profile so that automobile tires can roll over the disc without any difliculty. Mounted upon a surrounding planar surface 66, such as a roadway, driveway, or other surface carrying automobile traffic, the upper surface of disc 65 then becomes itself a traffic-bearing surface.

As shown in FIG. 3, light cell 27 is located at the center of the disc with its upper surface substantially flush with the top surface of disc 65 and is held in place in the disc by a body of cement 67 which acts not only to secure the light cell in place but also as a sealant to enclose and insulate the connections to the terminals of the light cell. Electrical connections to light cell 27 are preferably effected by a pair of wires in a fiat, tape-like conductor 68 which, because of its shape, offers a minimum projection above the surrounding tratfic surface and also is easily fastened to a street or roadway by pressure-sensitive tape.'Such means of securing conductor 68 in place is secure but easily removable.

The light cell is shown in FIGS. 11 and 12 as having its top surface substantially flush with the top surface of disc 65, thus affording maximum light-gathering angle to the cell. Under the circumstances, the total solid light-gathering angle may be or more, and even closely approach a full ideal To obtain this maxi mum exposure angle, the light-transmitting window and the light control mask described in connection with other embodiments have both been eliminated. However, they both may be incorporated in the form of FIGS. 11 and 12, if desired.

The body of cement 67 is preferably of the non-hardening variety to absorb a certain amount of the shock imposed upon the light cell as an automobile tire or the like rolls over the light cell.

Installations of the type last-described may be used for a number of purposes where it is desired to sense the movement or the passage of a vehicle. For example, the light cell may be installed in this manner in a street to operate a trafiic counter or a trafi'ic signal as well as to operate an alarm or signal to alert personnel to the presence or movement of a vehicle. As a further example of the versatility of the last-described installation, there is shown in FIG. 1 a disc 65 mounted at each side of the doorway 70 into the service station office, which is typical of any building. Thus a person passing either of the light cells mounted in these discs would be sensed by the device and give rise to a signal from the alarm in box 19. In this instance, the light cells are not mounted on a horizontal surface but on a vertical face of a building wall with the axes of the cells horizontal; but they can be designed to be sufficiently responsive to the passage nearby of a person entering or leaving the building through doorway 70. In order to insure adequate shadow to produce a triggering response, a flood light 71 is usually directed upon the light cell so that the triggering shadow will impinge upon the sensor as the object passes by.

From the foregoing disclosure, it will be understood that various changes may be made in the arrangement and construction of the elements of the present invention, and, accordingly, it is to be understood that the above description is considered as illustrative of, rather than limitative upon, the invention as defined by the appended claims.

I claim:

1. A system for detecting the proximity of a light obstructing body of a wheeled vehicle or other object, comprising:

a photoelectric cell having a light receiving face;

means for mounting said cell adjacent a traffic engaging surface, including a tubular supporting structure having a light-admitting opening and containing the cell with said face at said opening and substantially flush with an exterior surface of the tubular supporting structure, the size of the opening in relation to its distance from the light receiving face admitting light to the face over an unobstructed solid angle of more than about 90 with the apex of the solid angle located proximate said face.

2. A system as in claim 1 in which the solid angle is more than 120.

3. A system as in claim 2 which also includes light attenuating means within the tubular structure and over thviel light cell for varying the light transmission to the co 4. A system as in claim 3 in which the light attenuating means comprises a pair of light-polarizing discs that are relatively rotatable to vary light transmission therethrough.

5. A system as in claim 1 which also includes a vehicle supporting body over which vehicles pass and in which the tubular structure is embedded with the light admitting opening therein substantially horizontal in the path of vehicular traffic, and the axis of the tubular structure being substantially vertical and the light receiving face being directed upwardly.

6. A system as in claim 1 which also includes a thin disc receiving the tubular supporting structure and supported on said traflic-engaging surface, the disc having a vehicle wheel engaging upper exterior surface on and over which trafiic can pass, the light receiving face being substantially flush with the upper surface of the disc.

7. A system as in claim 1 that also includes an electric circuit connected to the photoelectric cell and including a signal responsive to a change in the light incident on the cell.

8. A vehicle sensing system according to claim 7 which also includes a mask over the photoelectric cell trans- Initting a predetermined amount of light to the cell.

9. An installation of a photoelectric cell in a driveway that comprises:

a tubular member set into the driveway and terminating below the surface of the driveway;

a housing slidably received in the tubular member and supported thereby with one end thereof substantially flush with the upper surface of the driveway;

'a photoelectric cell in the housing adjacent a lighttransmitting opening in the housing; and

an electric conductor leading into the tubular member and connected to the cell, there being sufficient slack in the conductor within the tubular member to permit the housing to be withdrawn from the tubular member.

10. An installation of a photoelectric cell according to claim 9 in which the housing has a terminal flange resting on the end of the tubular member, the axial thickness of the flange being substantially equal to the distance the end of the tubular member is recessed below the driveway surface.

11. An installation of a photoelectric cell according to claim 9 in which the housing is open at its lower end,

and which includes a conduit communicating with said lower end of the tubular member and containing said conductor.

12. An installation of a photoelectric cell as in claim 9 in which the tubular member has a laterally facing opening through which the conductor extends.

13. In combination,

a driveway including a generally horizontal slab,

a conduit extending generally horizontally below the level of the slab surface and having an end portion bent upwardly to terminate substantially at said surface,

a photo-electrical signal producing means slidably received within the open end of said conduit and located below the level of said surface in such relation to the zone directly above the slab as to produce an electrical signal in response to detection of a vehicle in said zone, and

means including an electrical device remote from said signal producing means and an electrical cable extending generally horizontally in said conduit and connected to said signal producing means and said electrical device to pass said signal from the producing means to the electrical device.

14. The combination of claim 13 including means supporting the signal producing means within said conduit end portion for upward removal therefrom above the surface of the slab while the conduit remains in fixed position relative to the slab.

15. The combination of claim 13 including gasoline pumping apparatus adjacent said driveway.

References Cited UNITED STATES PATENTS 2,489,113 11/1949 Veenstra 340-38 2,907,993 10/ 1959 Mathisen 340-228 2,525,824 10/1950 Nagel 340-38 1,764,368 6/1930 Thomas 340-38 2,653,309 9/1953 Hausz 340-38 THOMAS B. HABECKER, Primary Examiner US. Cl. X.R. 

